In electrochemical processes it is essential to ensure a uniform distribution of the current over the surface of the electrode. The uniform distribution depends on the throwing power of the electrolyte and on the homogeneity of the electrodes. The throwing power will be improved as the area on which the flux lines are incident on the counterelectrode is increased.
Although an inadequate throwing power can be increased by an increase of the electrode spacing, this will also increase the voltage drop of the cell. Inhomogeneities of the electrode surface will result in a deformation of the flux lines. For these reasons the distance between the electrode plates, i.e. the distance between the anode and cathode, is of essential significance.
In an ideal case the confronting surfaces of the two electrodes are parallel. The provision of parallel planar surfaces is a requirement for efficient cell operation because a uniform distribution of the electric current can be ensured and local overheating can be avoided only in that case.
In order to minimize the voltage drop and thus to reduce the energy consumption, the distance between the anode and cathode should be minimized. While all these requirements can be met in a relatively simple manner in small laboratory cells, difficulties are involved in the design of large industrial units if the theoretical requirements are to be met in a perfect manner.
Furthermore, cells become more sensitive to deviations from planar parallelism and to a deformation of the flux lines as the size of the cells increases. To avoid an accelerated destruction of the ion exchange membrane, it is generally necessary to limit the height of the electrodes, to provide a substantial distance between the electrodes of the cell, and to limit the electric current density although this will decrease the energy yield and the productivity of the electrolytic cell.
In order to reduce these disadvantages of electrolytic cells having membranes and vertical electrodes, it is conventional to use electrodes which have openings for the escape of the reaction gases. Such electrodes can be perforated or can consist of wire mesh or expanded metal. The disadvantages of these electrodes derive, inter alia, from the smaller active surface, the lack of mechanical stability and the loss of high-grade coating material on the rear of the electrodes.
Membrane cells having ion exchange membranes are usually provided with a frame structure which is as rigid as possible and in which the electrodes are rigidly mounted, in most cases by welded joints. In order to ensure that the electrodes are planoparallel within the close tolerance range which is required, on the one hand, and that a large number of such frames can be joined to form a leakage-free electrolyser which is similar to a filter press, the contact surfaces of the frames must also be machined in expensive operations.
In accordance with a proposal known from German Patent document DE-AS 20 59 868 gas-forming membrane cells have also been provided with platelike vertical electrodes consisting each of a plurality of plates formed with surfaces for guiding the gas which has been evolved and is to be discharged. The inclination of the guide plate or guiding surface necessarily involves different distances from the active surface to the counterelectrode and particularly local temperature increases may easily result in a warping of the delicate partitions, which are poor conductors of heat. It is also not possible to provide between the entire active surface of the electrode and the counterelectrode the small distance which would be desirable from the energy point of view.